Reducing fouling in oxidative dehydrogenation process

ABSTRACT

Reducing plugging of compressor discharge lines in oxidative dehydrogenation processes by maintaining high velocities in compressor discharge lines and optionally spraying water into the lines.

United States Patent Woerner [54] REDUCING FOULING IN OXIDATIVE DEHYDROGENATION PROCESS [72] Inventor: Rudolph C. Woerner, 6438 Brookside, Houston, Tex. 77023 [22] Filed: Nov. 14, 1968 [21] Appl. No.: 775,862

[52] US. Cl. ..260/680 E, 260/683.3 [51] Int. Cl ..C07c 5/18 [58] Field of Search ..208/48; 260/666.5, 680 E, 683.3,

OXYGEN,

NON CONDENSABLE GASES, ORGANIC COMPOUND ZONE A DEHYDROGENATION [is] 3,683,042 51 Aug. 8, 1972 3,308,201 3/1967 Bowers et al. 260/68 1.5

Primary Examiner-Paul M. Coughlan, Jr. Attorney-G. Baxter Dunaway [57] ABSTRACT Reducing plugging of compressor discharge lines in oxidative dehydrogenation processes by maintaining high velocities in compressor discharge lines and optionally spraying water into the lines.

10 Claims, 1 Drawing Figure WAT ER ZONE B WATE R CONDENSATION COMPRESSION ZONE C REDUCING FOULING IN OXIDATIVE DEHYDROGENATION PROCESS BACKGROUND OF THE INVENTION 1. Field of the Invention.

This Application relates to the oxidative dehydrogenation of organic compounds in vapor phase by a process wherein dehydrogenation is accomplished by reacting oxygen or a source of oxygen with hydrogen from an organic compound in order to dehydrogenate the compound. The reactor effluent gases are purified by a process including compression.

2. Description of the Prior Art.

It is known to dehydrogenate organic compounds by contacting the organic compound at an elevated temperature with oxygen, such as disclosed in US. Pat. Nos. 3,270,080, 3,303,234, 3,303,235, 3,303,236, 3,303,238, 3,308,182 through 3,308,201, 3,324,195, 3,334,152 and 3,342,890.

The dehydrogenation zone effluent from these oxidative dehydrogenation processes is cooled such as by quench, waste heat boilers and the like and generally the next step is to remove a major portion of the water by condensation. Thereafter'the gases are compressed in a compressor. However, in these processes considerable difficulty has been encountered directly downstream from the compressors as severe fouling of the compressor discharge lines has been experienced. This line fouling is evidenced by a pressure build-up in the discharge line. For example, prior to the use of a compressor system for the compression of effluent gases from an oxidative dehydrogenation reaction, the system had been used for the compression of gases obtained from a conventional non-oxidative dehydrogenation process. Even though there was some fouling of compressor discharge lines when gases from non-oxidative dehydrogenation processes were utilized, there was not evident a rapid build-up in pressure due to fouling and plugging. Yet when the same compressor. system was employed to compress effluent gases from oxidative dehydrogenation processes, the discharge lines fouled and plugged at an alarming rate and consequently the unit had to be shut down for maintenance. Inspection of these lines reveals an almost complete plugging with a polymeric type of material. The disassembly and cleaning of these lines is laborious and costly. Furthermore, when the compressors are operated with a partially plugged line, the efficiency and capacity of the compressor is correspondingly reduced. It was therefore an object of this invention to provide a means to minimize fouling and plugging in compressor discharge lines.

3. DESCRIPTION OF PREFERRED EMBODIMENTS.

According to this invention, the pressure build-up in the discharge lines has been greatly reduced by providing for a gaseous flow rate in the discharge line of at least 20 feet per second. Also as another embodiment of this invention, the discharge line may be sprayed with water under conditions such that at least a portion of the water spray remains in the liquid phase.

The reason for the fouling in the compressor discharge line is not fully understood. However, it is believed that the main source of fouling is from reaction products and polymers of various oxygenated compounds present in the compressed gaseous stream.

One preferred embodiment of the invention is illustrated in the drawing.

A gaseous mixture of the compound to be dehydrogenated, oxygen, noncondensable gases and perhaps steam are fed by line 1 to the dehydrogenation zone A. Preferably, the oxygen is supplied as air. The dehydrogenation reaction may be conducted in the absence of contact catalysts, but better results are obtained if the reaction is conducted in the presence of metal or metal compound catalysts, such as disclosed in the patents cited herein. The dehydrogenation reactor may be a fixed or fluid bed reactor. The conditions of reaction may be as disclosed in any of the cited patents such as US. Pat. No. 3,334,152. For convenience, the invention will be illustrated for the dehydrogenation of hydrocarbons and with a process where oxygen is fed to the reactor but it is understood that other dehydrogenatable organic compounds may be substituted in the example and that the oxygen may be supplied by a solid oxidant. It is also understood that it is not essential to have present noncondensable gases.

The effluent 2 from the dehydrogenation zone will contain the impure unsaturated hydrocarbon products, various impurities including oxygenated hydrocarbons, noncondensable gases and perhaps unconverted hydrocarbon, oxygen and steam. When air is used as the source of oxygen, nitrogen will be present in relatively large quantities as a noncondensable gas. Steam may be present in an amount up to 96 mol percent of the total effluent, such as from about 5 to 96 mol percent. The organic phase including dehydrogenated product, any unreacted feed, oxygenated hydrocarbons, polymer and tar and precursors thereof and any organic decomposition products usually range from about 1 to 50 mol percent of the effluent and generally will be within the range of or about 3 to or mol percent of the effluent. The noncondensable gases*(*The term noncondensable or inert noncondensable gases refers to those gases, other than hydrocarbons, such as nitrogen, CO and CO, which do not condense under the conditions encountered), such 40 to 80 mol percent.

The effluent gases 2 leaving the dehydrogenation zone will generally be at a temperature of about or greater than 600 F. or 700 to 1600 F. depending upon the particular dehydrogenation process. The reactor effluent may be cooled by any means or combination of means in cooling and condensation zone B as by quenching, waste heat boilers, condensers, vapor separators, and the like in any sequence. Preferably the major portion of any water present in the effluent will be removed as condensed steam from the gaseous effluent during this cooling and condensation operation. This cooled gaseous stream 3 may preferably then be compressed in compression zone C. The invention is not restricted to the particular processes prior to compression zone C. For example, an oil quench or other step may be included.

The gaseous composition 3 to be fed to compression zone C will usually comprise, exclusive of any water present, about or from 3.5 to mol percent of unsaturated organic compound such as hydrocarbon, about or from 0.0005 to 2.5 mol percent of carbonyl compounds**(**Except where expressed otherwise, all references in this Application are to overall quantities of carbonyl compounds as determined by ASTM Method D-l089 and reported as acetaldehyde. Generally, the carbonyl compounds will have from two to eight carbon atoms, e.g., from two to six carbon atoms when a C to C compound is being dehydrogenated, and will have from 1 to 2 carbonyl groups), and optionally about or from 20 to 93 mol percent of noncondensable gases (i.e., noncondensable under the conditions at point 3), all based on the total mols of gaseous composition 3 being fed to compression zone C, exclusive of any water. Included in the noncondensable gases will be any nitrogen, oxygen, CO or CO and the like. The oxygen content may vary, but suitably will be less than 10 mol percent of 3. Steam may also be present in 3 in an amount from to 20 or up to such as 50 mol percent or more of the gaseous composition 3. Also present in the gaseous mixture 3 may be hydrocarbon by-products and unconverted hydrocarbons such as olefins or saturated hydrocarbons.

A preferred composition 3 to be fed to compression zone C will comprise, exclusive of any water present, about or from 5 to 65 mol percent of unsaturated hydrocarbons, about or from 0.005 to 1.2 mol percent of carbonyl compounds and about or from 45 to 89 mol percent of the noncondensable gases. A particularly preferred composition 3 contains about or from 8 to 65 mol percent butadiene-l,3, about or from 0.1 to 40 mol percent butene, and about or from 40 to 75 mol percent nitrogen. The composition of the compressed gases at 4 may be within the same ranges as given for point 3.

Compression in compression zone C may be by any suitable mechanical compressors such as reciprocating or centrifugal compressors. Compressors conventionally employed in the recovery of butadiene-l,3 are suitable such as Clark reciprocating compressors. The pressure and temperature of the gases discharging from the compressors will depend upon the particular compressor employed, the pressure and the type of equipment downstream from the compressor, the temperature of cooling water available and the like but typically will be at a temperature of at least 125 F. and a pressure of at least 75 p. s.i.g. but generally the temperature will be at least 175 F. and the pressure at least 100 p.s.1. g.

According to this invention the gaseous flow rate in the discharge line is maintained at a flow rate of at least feet per second and preferably at least about or feet per second. This flow rate may be provided by suitably sizing the discharge line. The flow rate referred to is the maximum rate in the line from the compressor to the point at which the gases are cooled in a cooler of any type such as a heat exhanger or direct contact cooler. Of course, the stated flow rate may not be achieved immediately at the point of discharge from the compressor because of the necessity to reduce line sizes and perhaps to provide for means to reduce compressor vibration. At any rate, the referred to flow rate will generally be maintained in the major portion of the distance the gases travel from the compressor discharge to the first cooler.

The water spray(s) which constitutes a preferred embodiment of this invention may be installed at any point in the compressor discharge line. One or more sprays may be employed and any suitable type of spray nozzles may be employed. Preferably the water spray is concurrent with the flow of gases and the water pressure is high enough that some of the spray reaches the pipe walls. The conditions of temperature and flow rate of the water spray are controlled such that the water spray will at least partially, and preferably predominately, remain in the liquid phase until the gases contact the next piece of cooling equipment. Preferably the flow pattern is such that a major portion of the inside circumference of the line is contacted.

The gases from the compressor discharge may optionally be cooled by any means such as a shell and tube heat exchanger or in any type of equipment or apparatus for intimately contacting gases and liquids, such as tray columns including cross-flow plate and counterflow plate types, bubble cap columns, packed columns and spray systems including spray towers (open or packed), cyclonic spray towers, venturi scrubbers, and so forth. Thereafter, the gases may be treated to further separate and purify the gases such as by extractive distillation, C A A extraction, fractional distillation and the like.

The process of this invention may be applied to the recovery of products produced by the dehydrogenation of a wide variety of organic compounds. Such compounds normally will contain from two to 20 carbon atoms, at least one H H I I grouping, a boiling point below about 350 C., and such compounds may contain other elements, in addition to carbon and hydrogen such as oxygen, halogens, nitrogen and sulphur. Preferred are compounds having from two to 12 carbon atoms, and especially preferred are compounds of three to six or eight carbon atoms.

Among the types of organic compounds which may be dehydrogenated by means of the process of this invention are nitriles, amines, alkyl halides, ethers, esters, aldehydes, ketones, alcohols, acids, alkyl aromatic compounds, alkyl heterocyclic compounds, cycloalkanes, alkanes, alkenes, and the like. Illustration of dehydrogenations include propionitrile to acrylonitrile, propionaldehyde to acrolein, ethyl chloride to vinyl chloride, methyl isobutyrate to methyl methacrylate, 2- chlorobutene-l or 2,3 dichlorobutane to chloroprene, ethyl pyridine to vinyl pyridine, ethylbenzene to styrene, isopropylbenzene to a-methyl styrene, ethylcyclohexane to styrene, cyclohexane to benzene, methane to ethylene and acetylene, ethane to ethylene to acetylene, propane to propylene or methyl acetylene, allene, or benzene, isobutane to isobutylene, n-butane to butene and butadiene-l,3, butene to butadiene-l,3 and vinyl acetylene, methyl butene to isoprene, cyclopentane to cyclopentene and cyclopentadiene-l,3, n-octane to ethyl benzene and orthoxylene, monomethylheptanes to xylenes, propane to propylene to benzene, ethyl acetate to vinyl acetate, 2,4,4-tn'methylpentane to xylenes, the formation of new carbon to carbon bonds by the removal of hydrogen atoms such as the formation of a carbocyclic compound from two aliphatic hydrocarbon compounds or the formation of a dicyclic compound from a mono cyclic compound having an acyclic group such as the conversion of propene to diallyl. Representative materials which are dehydrogenated by the novel process of this invention include ethyl toluene, alkyl chlorobenzenes, ethyl naphthalene, isobutyronitrile, propyl chloride, isobutyl chloride, ethyl fluoride, ethyl bromide, n-pentyl iodide, ethyl dichloride, 1,3 dichlorobutane, 1 ,4 dichlorobutane, the chlorofluoroethanes, methyl pentane, methylethyl ketone, diethyl ketone, n-butyl alcohol, methyl propionate, and the like.

Suitable dehydrogenation reactions are the following: acyclic compounds having four to five non-quartemary contiguous carbon atoms to the corresponding olefins, diolefins or acetylenes having the same number of carbon atoms; aliphatic hydrocarbons having six to 16 carbon atoms and at least one quarternary-carbon atom to aromatic compounds, such as 2,4,4-trimethylpentene-l to a mixture of xylenes; acyclic compounds having six to 16 carbon atoms and no quarternary carbon atoms to aromatic compounds such as n-hexane or the n-hexenes to benzene; cycloparaffins and cycloolefins having five to eight carbon atoms to the corresponding olefin, diolefin or aromatic compound, e.g., cyclohexane to-cyclohexene or cyclohexadiene or benzene; aromatic compounds having eight to 12 carbon atoms including one or two alkyl side chains of two to three carbon atoms to the corresponding aromatic with unsaturated side chain such as ethyl benzene to styrene.

The preferred compounds to be dehydrogenated are hydrocarbons with a particularly preferred class being acyclic non-quartemary hydrocarbons having three or four to five contiguous carbon atoms or ethyl benzene and the preferred products are n-butene-l or 2, butadiene-1,3, vinyl acetylene, 2 methyl-l-butene, 3- methyl-l-butene, 3-methyl-2-butene, isoprene, styrene or mixtures thereof. Especially preferred as feed are nbutene-l or 2 and the methyl butenes and mixtures thereof such as hydrocarbon mixtures containing these compounds in at least 50 mol percent.

The organic compound to be dehydrogenated is contacted with oxygen in order for the oxygen to oxidatively dehydrogenate the compound. The oxygen may be supplied to the organic compound from any suitable source as by feeding oxygen to a dehydrogenation zone for example as disclosed in U.S. Pat. No. 3,207,810 issued Sept. 21, 1965. Oxygen may be fed to the reactor as pure oxygen, as air, as oxygen-enriched air, oxygen mixed with diluents, and so forth. Oxygen may also be supplied by means of a transport or moving oxidant type of process such as disclosed in U.S. Pat. No. 3,050,572 issued Aug. 21, 1962 or U.S. Pat. No. 3,118,007 issued Jan. 14, 1964. The term oxidative dehydrogenation process when used herein means a process wherein the predominant mechanism of dehydrogenation is by the reaction of oxygen with hydrogen.

The amount of oxygen employed may vary depending upon the desired result such as conversion, selectivity and the number of hydrogen atoms being removed. Thus, to dehydrogenate butane to butene requires less oxygen than if the reaction proceeds to produce butadiene. Normally oxygen will be supplied (including all sources, e.g., air to the reactor or solid oxidant to the reactor) in the dehydrogenation zone in an amount from about 0.2 to 1.5, preferably 0.3 to 1.2, mols per mol of H being liberated from the organic compound. Ordinarily the mols of oxygen supplied will be in the range of from 0.2 to 2.0 mols per mol of organic compound to be dehydrogenated and for most dehydrogenations this will be within the range of 0.25 to 1.5 mols of oxygen per mol of organic compound.

Halogen or other additives may be present in the dehydrogenation step such as disclosed in the above cited patents, e.g., U.S. Pat. No. 3,334,152 issued Aug. 1, 1967. Means for separating halogen may also be incorporated in the dehydrogenation reactor or downstream.

Preferably, the reaction mixture contains a quantity of steam or diluent such as nitrogen with the range generally being between about 1 or 2 and 40 mols per mol of organic compound to be dehydrogenated.

The temperature for the dehydrogenation reaction generally will be at least about 250 C., such as greater than about 300 C. or 375 C., and the maximum temperature in the reactor may be about 700 C. or 800 C. or perhaps higher such as 900 C. under certain circumstances. However, excellent results are obtained within the range of or about 350 to 700 C., such as from or about 400 C. to or about 675 C. These temperatures are measured at the maximum temperature in the dehydrogenation zone.

The remaining conditions, catalysts, flow rates and the like for oxidative dehydrogenation are known to those skilled in the art and may be e.g., as disclosed in U.S. Pat. No. 3,334,152 issued Aug. 1, 1967, or any of the remaining patents cited herein.

EXAMPLE 1 The invention can best be illustrated by a specific example. Reference is made to the drawing for the various pieces of equipment and streams. A hydrocarbon stream comprising butene-2 as the major component is oxidatively dehydrogenated to butadiene-1,3 in reactor A. The feed 1 to the reactor includes air and steam. The efiluent 2 from the reactor comprises butadiene- 1,3, unreacted butene, carbonyl compounds, steam, noncondensable gaseous components such as nitrogen and various dehydrogenation by-products such as C0 The efiluent is cooled and most of the water is removed in the steam condensation zone B. The gaseous stream is then compressed in the compression zone C. The compressed gases at point 4 comprise by mol percent approximately a total of 64.5 percent noncondensable gases (mostly nitrogen, but also includes the other residual gases of air, as well as CO and CO and 32.3 percent hydrocarbons. The hydrocarbon portion is primarily C s with butadiene-1,3 being the major component. The composition also contains 2.6 percent water and by chromatographic analysis 0.15 percent acetaldehyde, 0.01 percent crotonaldehyde, 0.05 percent acrolein and 0.01 percent methacrolein. The gases are at a temperature of 280 F. and 141 p.s.i.g.

To illustrate the prior art process, the gases are first discharged into a 14 inch line which results in a flow 20 p.s.i.g. between the points.

The invention is illustrated by certain changes which are made. The line between points 4 and 6 is replaced with an 8 inch line so that in approximately the first 37 feet of the line the velocity of the gases is 37 feet per second. Water is sprayed into the line at point 5 which is approximately 8 feet from the discharge from the compressor. The water is sprayed concurrently with the gas flow at a rate of 3.5 gallons per minute with the pressure of the water being 230 p.s.i.g. and the temperature of the water being 205 F. A further reduction in size is installed at point 6 to a 6 inch line to result in a flow rate of 65 feet per second. Approximately 1 16 feet of the original line is replaced with this 6 inch line which runs to point 7. Water was also sprayed concurrently at point 6 under these same conditions of water temperatures and pressure as at point 5 but at a rate of about 11 gallons per minute. Under these new conditions, the pressure at point 4 initially is 159 p.s.i.g. and at point 7 is 157 p.s.i.g. for a pressure drop of 2 p.s.i.g. After a period of operation of about 9 months the pressure at point 4 is 168 p.s.i.g. (with the rise in pressure at point 4 due to other factors downstream from the line in question) and at point 7 is 166 p.s.i.g. which amounts to the same pressure drop of only 2 p.s.i.g. No attempt was made to reduce fouling between point 7 and point 8 and the pressure built up slightly, such as about 1 to 2 p.s.i.g., over this 9 month period to give an overall build-up of 1 to 2 p.s.i.g. from point 4 to point 8.

EXAMPLE 2 Example 1 is repeated with the elimination of the water spray at point 5. Little build-up of pressure is evident over a period of months.

EXAMPLE 3 Example 1 is repeated with the elimination of both water sprays and favorable results are still obtained.

EXAMPLE 4 Example 1 is repeated with the exception that a mixture comprising 60 mol percent 2-methyl pentene-l and 2-methyl pentane is dehydrogenated to isoprene and the effluent gases are recovered and compressed as in Example 1 with similar favorable results.

lclaim:

l. A process for the preparation of unsaturated hydrocarbon compounds by the oxidative dehydrogenation of a feed of acyclic non-quarternary hydrocarbons having from three to five carbon atoms with reduced pressure buildup and fouling in the discharge lines from the compressors by a process wherein the said feed is dehydrogenated, cooled and compressed in a compressor to produce a discharge fifiiisi 31% geflll diufffi l iir al ififi carbonyl compounds and from 20 to 93 mol percent non-condensable gases at a temperature of at least 125 F. and at a pressure of at least p.s.i.g. and discharging the said discharge gaseous composition into a discharge line having an original pipe diameter such that the velocity of the said composition will be at least 25 feet per second.

2. A process for the preparation of butadienel ,3 by the oxidative dehydrogenation of a feed of acyclic nonquartemary hydrocarbons having four carbon atoms with reduced pressure buildup and fouling in the discharge lines from the compressors by a process wherein the said feed is dehydrogenated, cooled and compressed in a compressor to produce a discharge gaseous composition comprising exclusive of water from 3.5 to mol percent unsaturated hydrocarbon including butadiene-1,3, about 0.0005 to 2.5 mol percent carbonyl compounds and from 20 to 93 mol percent non-condensable gases at a temperature of at least F. and at a pressure of at least 75 p.s.i.g. and discharging the said discharge gaseous composition into a discharge line having an original pipe diameter such that the velocity of the said composition will be at least 25 feet per second.

3. The process of claim 1 wherein an aqueous spray is sprayed into the said discharge line under conditions such that at least a portion of said aqueous spray remains in the liquid phase in said discharge line.

4. The process of claim 1 wherein the said effluent gases in the discharge line comprise about 0.0005 to 2.5 mol percent carbonyl compounds.

5. The process of claim 1 wherein the said organic compound is a hydrocarbon of four to five carbon atoms having a straight chain of at least four carbon atoms.

6. The process of claim 1 wherein the said organic compound is selected from the group consisting of nbutene, n-butane and mixtures thereof and the said dehydrogenated organic compound comprises butadiene-1,3.

7. The process of claim 1 wherein the said flow rate of the effluent gases is at least 30 feet per second.

8. The process of claim 1 wherein the said temperature if at least F. and the said pressure is at least 100 p.s.i. g.

9. The process of claim 1 wherein the said discharge line is no greater than 8 inches in diameter.

10. A process for the preparation of butadienel ,3 by the oxidative dehydrogenation of n-butene by a process with reduced pressure buildup and fouling wherein the said n-butene is dehydrogenated, cooled and compressed in a compressor to produce a discharge gaseous composition comprising exclusive of water from 8 to 65 mol percent butadiene-l,3, 0.1 to 40 mol percent butene and from 40 to 75 mol percent nitrogen at a temperature of at least 175 F. and at a pressure of at least 100 p.s.i.g., discharging the said gaseous composition into a discharge line having an original pipe diameter such that the velocity of the said composition will be at least 30 feet per second and spraying an aqueous spray into said discharge line.

mg UNITED STATES PATENT OFFICE @ERTIFICATE 0F @QRRECHUN Patent-No. 3,683,042 Dated August 8, 1972 I Inventofls) I Ru olph C. Woerner It is certified that error appears in the above-identified patent .and that said Letters Patent are hereby corrected as shown below:

[73] Assignee: Petro-Tex Chemical Corporation, Houston,

Texas Signed and sealed this 9th. day of January 1973.

(SEAL) Attest:

ROBERT GOT'I'SCHALK Commissioner of Patents EDWARD M.FLETCHER, JR. Attesting Officer 

2. A process for the preparation of butadiene-1,3 by the oxidative dehydrogenation of a feed of acyclic non-quarternary hydrocarbons having four carbon atoms with reduced pressure buildup and fouling in the discharge lines from the compressors by a process wherein the said feed is dehydrogenated, cooled and compressed in a compressor to produce a discharge gaseous composition comprising exclusive of water from 3.5 to 80 mol percent unsaturated hydrocarbon including butadiene-1,3, about 0.0005 to 2.5 mol percent carbonyl compounds and from 20 to 93 mol percent non-condensable gases at a temperature of at least 125* F. and at a pressure of at least 75 p.s.i.g. and discharging the said discharge gaseous composition into a discharge line having an original pipe diameter such that the velocity of the said composition will be at least 25 feet per second.
 3. The process of claim 1 wherein an aqueous spray is sprayed into the said discharge line under conditions such that at least a portion of said aqueous spray remains in the liquid phase in said discharge line.
 4. The process of claim 1 wherein the said effluent gases in the discharge line comprise about 0.0005 to 2.5 mol percent carbonyl compounds.
 5. The process of claim 1 wherein the said organic compound is a hydrocarbon of four to five carbon atoms having a straight chain of at least four carbon atoms.
 6. The process of claim 1 wherein the said organic compound is selected from the group consisting of n-butene, n-butane and mixtures thereof and the said dehydrogenated organic compound comprises butadiene-1,3.
 7. The process of claim 1 wherein the said flow rate of the effluent gases is at least 30 feet per second.
 8. The process of claim 1 wherein the said temperature if at least 175* F. and the said pressure is at least 100 p.s.i.g.
 9. The process of claim 1 wherein the said discharge line is no greater than 8 inches in diameter.
 10. A process for the preparation of butadiene-1,3 by the oxidative dehydrogenation of n-butene by a process with reduced pressure buildup and fouling wherein the said n-butene is dehydrogenated, cooled and compressed in a compressor to produce a discharge gaseous composition comprising exclusive of water from 8 to 65 mol percent butadiene-1,3, 0.1 to 40 mol percent butene and from 40 to 75 mol percent nitrogen at a temperature of at least 175* F. and at a pressure of at least 100 p.s.i.g., discharging the said gaseous composition into a discharge line having an original pipe diameter such that the velocity of the said composition will be at least 30 feet per second and spraying an aqueous spray into said discharge line. 